Effects and Absorption of Sethoxydim on Excised Root Tips of Corn

Z. Naturforsch. 4 8c , 2 8 8 -2 9 3 (1993); received November 3, 1992 Sethoxydim, Growth Inhibition, Cell Cycle, Fatty Acids The mechanism of selective herbicidal action of sethoxydim was investigated by using cul­ tured root tips of corn and pea. Sethoxydim inhibited the growth of susceptible corn root at concentrations of 3 nM and above, but did not affect that of pea at 0.1 m M . Meristematic cells in cultured roots were arrested at the G, and G 2 stages of the cell division cycle by sucrose star­ vation, and resumed growth and cell division (proliferation) upon sucrose addition. Corn root growth was not inhibited by sethoxydim even at 0.01 m M when the roots were arrested by su­ crose starvation. Corn roots that resumed growth upon sucrose provision were more sensitive to sethoxydim than those kept in constant growth condition. Better absorption of [l4C]sethoxydim into the meristematic region of corn roots was observed when cells were in the proliferative condition, which was not observed when cells were arrested by sucrose starvation. No stronger uptake of the herbicide was observed into pea meristems in either growth condi­ tion. In the cell cycle study, stronger absorption of [l4C]sethoxydim into the corn root meristem took place at a certain limited period prior to the S (D N A synthesis) stage. The physiolog­ ical effects and the better absorption of sethoxydim clearly depended on cell cycle progression of the corn root meristem, while fatty acid synthesis, as well as its inhibition by sethoxydim, was neither associated with cell cycle progression nor with stronger absorption of the herbi­ cide. The selective herbicidal action of sethoxydim may be caused by interference with selected stages (G, and/or the transition step between G, and S stages) of the cell division cycle, where affinity sites for the herbicide might be expressed.